Statistic

1. The heights of Grade 2 students are normally distributed with a mean of 105 cm and a standard deviation of 9 cm. Joey is a grade 2 student and his height is represented by a z-score of 0.7. Determine Joey's height, to the nearest tenth of a centimetre.

2. A tutor promises that 9% of her students will obtain an "A" on every test they write. For the last test, the mean mark was 67 and the standard deviation was 5. What mark is required to receive an "A" on the test? Use the calculator statistics functions and clearly document your calculator entries. Round your answer to the nearest whole number.

3.An advertisement for a new toothpaste states that 72% of users reported better dental checkups. The results of the poll are accurate within 4.2 percent points, 8 times out of 10.

a) State the confidence level of this poll.

b) Determine the confidence interval of the poll. Write your answer in two different ways.

c) If a group of 2000 people was surveyed, calculate the range of people who would report better dental checkups.

d) Explain why the margin of error would increase if the sample size of the poll decreased.